Well, in the case of current canon law…
Latins have to have a DL to fulfill obligation.
Easterns have to have a sunday or holy day DL, or a tradition of some other praxis, or enabling legislation for some other praxis.
The Byzantines universally have a vespers and matins tradition; further, certain feasts have an anticipatory combined vespers/DL tradition.
The Ruthenians and Ukrainians have a persistent use of anticipatory DL’s… 50 years gives it force of law as custom.
CCEO:
Canon 880
- Only the supreme authority of the Church can establish, transfer or suppress feast days and days of penance which are common to all of the Eastern Churches, with due regard for 3.
- The authority of a Church sui iuris which is competent to establish particular law can constitute, transfer or suppress feast days and days of penance for that Church sui iuris, however having sought the opinions of the other Churches sui iuris and with due regard for can. 40, 1.
- Holy days of obligation common to all the Eastern Churches, beyond Sundays, are the Nativity of our Lord Jesus Christ, the Epiphany, the Ascension, the Dormition of the Holy Mary Mother of God and the Holy Apostles Peter and Paul except for the particular law of a Church sui iuris approved by the Apostolic See which suppresses a holy days of obligation or transfers them to a Sunday.
Canon 881
- The Christian faithful are bound by the obligation to participate on Sundays and feast days in the Divine Liturgy, or according to the prescriptions or legitimate customs of their own Church sui iuris, in the celebration of the divine praises.
- In order for the Christian faithful to fulfill this obligation more easily, the available time runs from the evening of the vigil until the end of the Sunday or feast day.
- The Christian faithful are strongly recommended to receive the Divine Eucharist on these days and indeed more frequently, even daily.
- The Christian faithful should abstain from those labors or business matters which impede the worship to be rendered to God, the joy which is proper to the Lord’s day, or to the proper relaxation of mind and body.
Canon 883
- The Christian faithful who are outside the territorial boundaries of their own Church sui iuris can adopt fully for themselves the feast days and days of penance which are in force where they are staying.
- In families in which the parents are enrolled in different Churches sui iuris, it is permitted to observe the norms of one or the other Church, in regard to feast days and days of penance.
CIC (Roman)
Can. 1246
§1. Sunday, on which by apostolic tradition the paschal mystery is celebrated, must be observed in the universal Church as the primordial holy day of obligation. The following days must also be observed: the Nativity of our Lord Jesus Christ, the Epiphany, the Ascension, the Body and Blood of Christ, Holy Mary the Mother of God, her Immaculate Conception, her Assumption, Saint Joseph, Saint Peter and Saint Paul the Apostles, and All Saints.
§2. With the prior approval of the Apostolic See, however, the conference of bishops can suppress some of the holy days of obligation or transfer them to a Sunday.
Can. 1247
On Sundays and other holy days of obligation, the faithful are obliged to participate in the Mass.
Moreover, they are to abstain from those works and aVairs which hinder the worship to be rendered to God, the joy proper to the Lord’s day, or the suitable relaxation of mind and body.
Can. 1248
§1. A person who assists at a Mass celebrated anywhere in a Catholic rite either on the feast day itself or in the evening of the preceding day satisfies the obligation of participating in the Mass.
§2. If participation in the eucharistic celebration becomes impossible because of the absence of a sacred minister or for another grave cause, it is strongly recommended that the faithful take part in a liturgy of the word if such a liturgy is celebrated in a parish church or other sacred place according to the prescripts of the diocesan bishop or that they devote themselves to prayer for a suitable time alone, as a family, or, as the occasion permits, in groups of families.